Landracing Forum
Bonneville Motorcycle Speed Trials => Bville Motorcycle Speed Trials General Chat => Topic started by: gschuld on October 21, 2018, 07:15:35 PM
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So for fast modern bikes on the salt, say 170mph on up, 150 through 180 series tires seem most common on the rear. On classic class bikes in the 100-150mph range (or higher), narrower 110-130 rear tires appear to be more common.
Both make sense for no other reason than these were generally the rear tire sizes that these bike were designed to run on. Wheel offsets, chain alignment, etc factor in.
I understand the general theory of a fatter tire having a say, 1-1.5” wide contact patch, also has the issue of pressure build up on either side of that contact patch, as some point causing some lift(more so than a narrower tire). I have no idea how much and when these effects manifest themselves. Clearly wide rear tires are pushing bikes into the upper 200s, so they certainly work!
For a bike, for example(selfishly) in the 425lb bike plus 215lb rider range, 105-110 RWHP at sea level, in the 1000cc MCG class at 58” wheelbase, is there an advantage either way between a 110/120 series rear tire on a 3” rim and a 160 series rear tire on a 4.25” rim? Perhaps 120/130/140 tire on a 3.5” rim?
Obviously the wider rim/tire combo will weigh a bit more, but not that much more.
Thoughts appreciated...😉
George
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George, what size rim are you working with.... there are lots of opinions on tire size.... and width.... most high speed tires are available in 17 inch. I personally prefer the the smallest, narrowest front at the speed rating we need and near stock size in rear... of course we raced modern Suzy's so tires were easy...
I hope my buddy Ross (MC2032) chimes in here, but he switched to Sport Bike rims so he could get a better selection of tires for his bike.
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I’m kind of a hoarder for aluminum rims, as I’m dealing with 40 spoke wheels here with heavy gauge Buchannan SS spokes. I have two sets of completed wheels with 2.5x18 fronts, 3.5x18 rears.
I have 3 brand new Akront 4.25x18 rims, a new 3.0x18, etc. I’ve been looking for an excuse to build a set of rear wheels with the new 4.25x18 rims😉
I was looking at the Pirelli Angel GT tires for an example. W speed rated, dual compound, mostly for 17” sport bikes, but they carry a 110/70/18 and a 120/60/18 along with a 160/60/18 rear. I’d prefer to stick with 18s if possible as it represents all my stock on hand. Plus 17s just don’t quite look right to me on old bikes(personal preference)
Many riders say they use front tires, often in matching sizes, front and back. I could mount up a 120/70/18 to the 3.0x18 rim in the rear and use a 110/70/18 on the 2.5x18 up front. That would represent a “narrow” rear option. And likely a good reasonable option.
There is some debate I guess at to whether even HD spoke wheels are not a good idea depending on speed(and the quality, condition, and trueness on the spoke wheels I guess)
George
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If you can get tires rated for the speed you need then use them...
Be sure your spoke wheels are straight and true...
Alignment is very important at Bonneville.
You have plenty of time, do due diligence.... test everything you can.
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If you can get tires rated for the speed you need then use them...
Be sure your spoke wheels are straight and true...
Alignment is very important at Bonneville.
You have plenty of time, do due diligence.... test everything you can.
Yes, those Pirelli Angel GT tires are W rated. Which means 168mph plus(?)
Still uncertain about what that means in relation to the BMST rules. Does a W tire rating mean I’m good too UP TO 168mph, but not over?
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Radial tires on spoked rims are used on Triumph Bonnevilles as original equipment. This made me comfortable with the concept. My preference is to use a front and rear tire from the same manufacturer that are on the specified wheel position, front or rear, and designed to work together as a set for the application, load, and speed. My 1000cc bike with a 170 pound rider and 105 rear wheel horsepower is similar to your proposed setup. It uses Bridgestone Battleaxe BT023 radials on spoked wheels with a heavy duty Inoue front tube and a Bridgestone rear tube designated for use with a radial tire. The front and rear rim sizes are 2.5 x 19 and 3.5 x 17 respectively with ZR rated tires of proper sizes for those hoops. Cold tire pressure is the manufacturer's recommended maximum. No problems with wheel slip or reliability with this setup.
In response to another thread on this proposed bike, countershaft sprocket size is a minimum of 18 tooth and preferably 19 tooth to promote chain life.
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Thanks for the info. A friend who holds the MCG/MCF/MCGPS/MCFPS(135-147mph) records in the 750 classes is using a 16 and a 17 for primaries with a 520 chain in the same bike type(Honda CB750)
18 and 19 primaries would require rather large sprockets at the wheel with our final drive ratios and rpms. Like starting in the mid 50s in teeth on up to the low 60s of so. That’s doable, but far from ideal. Actually, I know I can’t fit a 19 tooth primary with an engine case protector installed, possibly not an 18 either. I’ll have to check.
George
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I’m kind of a hoarder for aluminum rims, as I’m dealing with 40 spoke wheels here with heavy gauge Buchannan SS spokes. I have two sets of completed wheels with 2.5x18 fronts, 3.5x18 rears.
I have 3 brand new Akront 4.25x18 rims, a new 3.0x18, etc. I’ve been looking for an excuse to build a set of rear wheels with the new 4.25x18 rims😉
I was looking at the Pirelli Angel GT tires for an example. W speed rated, dual compound, mostly for 17” sport bikes, but they carry a 110/70/18 and a 120/60/18 along with a 160/60/18 rear. I’d prefer to stick with 18s if possible as it represents all my stock on hand. Plus 17s just don’t quite look right to me on old bikes(personal preference)
Many riders say they use front tires, often in matching sizes, front and back. I could mount up a 120/70/18 to the 3.0x18 rim in the rear and use a 110/70/18 on the 2.5x18 up front. That would represent a “narrow” rear option. And likely a good reasonable option.
There is some debate I guess at to whether even HD spoke wheels are not a good idea depending on speed(and the quality, condition, and trueness on the spoke wheels I guess)
George
George,
I agree with you that aluminum rims with SS spokes represent the true classic look on our old bikes, but if I were you, I would just use those rims to rebuild a couple more classic riders. I've switched to cast 17" rims for a couple of reasons on my partially streamlined 150 mph BSA. Firstly, I just don't have good confidence in the inner tubes they make today and I have pinched too many of them during installation. Imagine that you unwittingly barely pinched one of yours on your race bike, you spend a lot of time and money just getting to the Salt, and you get a flat tire on one of your runs, maybe even a return run. Sure can ruin a good day.
Secondly, as I rebuild my own spoke wheels, rightly or wrongly, I seem to have trouble getting the wheels to true up better than 1/16" radially (out-of-round). Probably new Sun or Excel rims are better, but the older high-shouldered Borrannis just seem hard to get truly round. Cast rims, even junk yard ones, can be found to be within .005" of true which just seems better. Furthermore, speed rated 17" tires are easier to find and cheaper (sometimes free if you check your dealers take-off pile).
I use a 110/70 ZR17 up front with a 120/70 ZR17 in back.
At some point, you may have to choose between the classic look and speed you need to set that record.
Tom
P.S. Give my regards to Dennis and tell him to pay attention to my new TR250/BSAB25!
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Great info thanks. I tend to be stubborn regarding aesthetics. And generally to my logistical detriment. I simply appreciate the vintage style of these bikes, and although they can look quite nice with modern touches added in, it’s not my thing. I’m generally willing to give up some ultimate performance in an effort to keep the end result more pleasing to my eye. It’s an issue I should go to counseling for😎
But your remarks are very logical and follow a path that many others have followed. I will keep it in mind and potentially even come to my senses.
Next year is the 50th anniversary of the cb750(1969). So it is an extra incentive to run an actual 1969(non sandcast) CB750 and have it look a bit like a salt racer version of the factory bike. Cast wheels wouldn’t fit into my admittedly misguided and selfish grand “vision”
George
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George, chassis stability requires many things to be correct, such aerodynamics, weight distribution, suspension setup, chassis geometry, component condition, and tire compatibility. It is hard to locate the cause of instability if a problem occurs and more than one of these is wrong.
Often production based bikes set some the faster times at the meets. One does not give up a lot of performance to use a well setup and aligned standard chassis in good condition with tires designed for the purpose. Once this bike is working correctly things can be changed one at a time and tested. There will be a "known good" configuration to use as a reference point. Stability issues are much easier to rectify using this method.
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George, chassis stability requires many things to be correct, such aerodynamics, weight distribution, suspension setup, chassis geometry, component condition, and tire compatibility. It is hard to locate the cause of instability if a problem occurs and more than one of these is wrong.
Often production based bikes set some the faster times at the meets. One does not give up a lot of performance to use a well setup and aligned standard chassis in good condition with tires designed for the purpose. Once this bike is working correctly things can be changed one at a time and tested. There will be a "known good" configuration to use as a reference point. Stability issues are much easier to rectify using this method.
Thanks for your thoughts. Those are good points. I’m very fortunate to have a fellow racer with the same bike model also running modified, just in the next class down in displacement. He started with a lowered factory chassis, then to a slightly reraked neck and a modestly longer swingarm. Both setups were in his words “rock solid” in stability(in the 140s mph and counting). The only item I’ve considered outside his successful parameters is a wider rear rim/tire of nearly the identical diameter. If I make the trip, it may only be once. I intend to benefit from someone else’s 5 years worth of hard fought experience. And my pal Dennis has been a HUGE help.
Thanks Dennis😉
George
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Sorry, I am a little late to the party. Yes, I opted for late model import wheels (at least the front one for now) as tire selection was a whole lot better (there are almost no speed rated tires in stock Harley sizes). the craigslist donorcycle ponied up the front end (forks, triple trees, fender, wheel, handle bars, etc) all designed for speeds waaay faster than HD ever envisioned. so, swapping out HD stuff for rising sun products was an easy decision. the bike and this rider scale at apprx. 750 lbs with a 50/50 split front to back. traction has not been an issue so far but we are going to address that per the old adage "add power till the tires break loose then add weight till they don't. repeat till you are out of money"
The stock cast Gixxer wheel is straight and true, is tubeless and again, is easy to find tires to fit. i run 50 psi and the tires show almost no wear, the little thingies are still on the chicken strips. the last tire timed out with it's Minnie Pearl still attached.
To add to what stainless said about alignment, yes it is very important. at the '12 WOS meet my back wheel was out about three or four flats on the left side adjuster. bike dog tracked something fierce, almost wanted to swap ends. i had to hang off the bike to convince it to wander back to the centerline. fixed that before the next pass then when back home in the land of oz, i broke down the entire bike and reassembled while keeping everything plumb and square. bike has ridden like it is on a rail since. Hope this helps. go fast, have fun, be safe.
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Fortunately, I’m pleased with the quality of suspension upgrade options for out CB750. Racetrch cartridge eliminators and fork springs up front in the forks work very well, and quality rear shock options abound(I prefer dial a ride(adjustable rebound)vintage Koni alloy body shocks personally)
Your comments regarding carefull alignment is understood👍 Cb750 frames were sometimes a bit off from the factory and it isn’t unusual to realign them when being converted for vintage road racing. So chassis/swingarm alignment first, followed by careful alignment of the wheels.
Is it common to have the tires themselves tried/shaved to ensure perfect roundness?
George
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Nate Jones Tire Company, in SoCal, is a supplier of race tires, and they'll shave them for you -- per your specs! Nate is the tire guy on the Speed Demon and is (obviously) very familiar with land speed racing. I mean, when you place your shaving order you'll get asked what type of racing, what venue -- so the tire can be custom contoured for your personal needs.
Caution: My bike tires always look gross as all get out when I first get 'em back from Nate - but they worked fine so I guess the aesthetic cops aren't on patrol at Bville.
Another minor but cool value to getting tires from Cowboy Tire (another name, same company) is that it's easy to get them delivered to the salt. I send my empty wheels to him, they mount, balance, shave, and balance some more and then find someone or other that's going to the salt and will deliver the tires to my pit.
Yes, ask for vintage or special tires. They've got resources. . .and best of all, Nate advertises in the Rulebook - helps support our fun and games.
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I’ve read that W (168+)is currently the highest motorcycle DOT speed rating in use today. Y(186+) exists on paper at least but are there actually any tires out there officially with that rating?
And if one were to exceed 168mph on W(168+) tires, this is OK? Up to what point?
Thx,
George
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BMST the responsibility of tire choice is the riders
many of the current sportsbike tires will do 200 fairly safely ,
The tires used up at Bolivia for the 300mph attempts chunked but maintained structural integrity
If you choose wrong
https://www.youtube.com/watch?v=VrbgNNETjBY
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The rules suggest the tires must have a manufacturers speed rating up to the capability of your bike and/or up to the current record. I understand the 200 mph plus guys simply can't comply with this as sport bike tire manufacturers aren't offering tires with such a high rating. Y(186+mph) seems to be the highest speed rating and I haven't seen it actually used. I see plenty of W (168+mph) rates tires though.
In the classic 1000cc MPS Fuel class, with strong power and good traction and fairings, pretty strong mph numbers are possible.
George
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Pretty wild ride Greg... I guess you don't buy that tire anymore.... ugly vibration after the chunks started flying :-o ...
hey I noticed you short shifted 5th... :roll: good job keeping the paint on it
:cheers:
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Same tire Al had and his Vids look the same ,
The one i do like the Bridgestone BT003 they dont make any more and ours are about out of years
thinking of changing to the Dunlop slicks that Ralph was using
shortshifting yep noticed i do that if its wriggling with wheelspin , dont get enough runs at that speed to clean up bad habits
good paint was all about good luck, no skill required :-D
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I guess I should go look at my bike, but you can probably answer.... is the BT003 a dot or racing purposes tire? I noticed this year that they dropped the 10 year age out requirement for racing tires...
I think Ralph only changed one front in Bolivia.... several rears... but they all stayed structurally good... just chunked a little bit of rubber here and there. They did a lot better after he stopped using warmers.
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"racing" type street tire, meets SCTA needs and for us been a great tire since 2012,
Ralphs 1 tire per pass used them up pretty quick, but there probably the best out there at the moment that have been "tested"
Yes it was funny how they lasted better without the warmers, when i had always thought our chunking was a result of cold tearing
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Greg you mention Ralph using Dunlop tyres, are thay the Sportmax Q4 series ?
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N tec i think, KR series
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The mention of racing slicks bring up another question. I’ve read that some suggest that a hard compound tire is preferable to a soft compound tire. I believe the rational related to soft tires being more susceptible to excessive abrasion wear as a result of the slippage friction buildup on the salt. Is that a universally held opinion?
So for W rated DOT tires, does this generally mean that harder compound tires (tires designed with high mileage in mind, usually dual compound) are preferable?
I’m talking over 150 but under 200mph in his case FWIW.
George
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Not to sound like a cheap skate, but I went to an AMA race at Pacific Raceway in Kent Wa. and a couple of race teams GAVE me there take off front tires (and tried to give me the rears) for free. In the event that SCTA sees fit to let me run them on my lakester I have a stash. Best thing, they have most of the rubber worn off. I bought 2 new Pirrelli Dragon Super Corsa Pro tires several years back at a AMA race from the Pirrelli Tire trailer. The engineers looked at a Goodyear front dragster tire and mockingly concluded that if they ran over 300mph then their steel belted radial constructed tire should be good for 400. I mounted the tires (60lbs) and put them on my brake lathe and ground the sidewall and crown off of most of there rubber. Had about 4 dust pans of rubber on the floor. Used one of those sprint car tire grinding discs. Be careful!!! Lee Kennedy let me run them to 275 no issues. I put them on my car with no grease in the bearings and gravity balanced them. Smooth as...
If it was left up to me I wouldn't be be afraid to go 350 with them. P.S. they do look like the ones Slim described.
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George , my take on that is the soft tires chunk easier, seen a front "wet" race tire chunk in a pass when the rider was countersteering a side wind
i dont think grip changes much out there much due to tire compound, more the salt surface and how wet or dusty it is
Geo and here i am trying the skinny front runners on the bike to try and get a safe tire for over 250mph
Using a slow speed rotary sander polisher with 40 grit to make black dust and shape the tire
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I bought the hardest compound they made. After several heat cycles the used ones I have feel hard as rock. Mine didn't have rubber to chunk off. That's the trick. Saw a famous 400 mph player paint latex rubber over the CORDS of his tires back in the day. Worked just fine.